In conventional arts, as duplex modes in radio communication systems, there are known Frequency Division Duplex (FDD) for dividing uplink (UL) and downlink (DL) by frequency and Time Division Duplex (TDD) for dividing UL and DL by time (for example, see Non-Patent Literature 1). In FDD, an uplink signal and a downlink signal are transmitted and received with the same time and different frequencies. On the other hand, in TDD, an uplink signal and a downlink signal are transmitted and received with the same frequency and different times.
In TDD of an LTE (Long Term Evolution) system, there are defined UL/DL configurations each indicating a ratio between UL subframes and DL subframes in a radio frame (see FIG. 1). In the LTE system, as illustrated in FIG. 1, seven UL/DL configurations are defined.